A wide variety of systems employ two-cycle internal combustion engines as their power plants. One reason why two-cycle engines are utilized for these applications is because of their high specific output and relatively compact size. For example in substantially all watercraft applications, particularly those of the smaller type of pleasure craft and utility craft, the space available for the engine is quite restricted. Therefore, it is desirable to be able to utilize an engine that has high specific output and a compact configuration. This is particularly true in connection with outboard motors. As is well known, with an outboard motor the engine is positioned in the powerhead and the outboard motor is normally mounted in the transom of the watercraft which it propels. This obviously requires a compact power plant.
The compact and simple nature of two-cycle engines, however, gives rise to certain problems. Because of the scavenging system employed and the inherent overlap in the port timing, it is more difficult to control the exhaust emissions with two-cycle engines, particularly when the engine runs over a wide variety of speeds and loads. In addition, the lubricating system employed with two-cycle engines can, at times, also give rise to emission problems.
Therefore, there is an increasing desire to substitute four-cycle engines for two-cycle engines in watercraft propulsion systems. This trend is arising not only in outboard motors but also in the power plants for small watercraft such as personal watercraft that have also normally used two cycle engines. However, these applications do require compact engines and engines that provide high power outputs for their size.
It is, therefore, a principal object of this invention to provide an improved and compact power plant arrangement.
It is a further object of this invention to provide an improved, compact and yet high output engine that can be utilized for marine propulsion.
It is a still further object of this invention to provide an improved high output compact four-cycle internal combustion engine and watercraft propulsion system utilizing such an engine.
An engine which has the capability of providing high specific output is disclosed in U.S. Pat. No. 5,377,634 entitled "Compressor System For Reciprocating Machine", issued Jan. 3, 1995 in the name of the one of the inventors hereof and which application is assigned to the Assignee hereof. In that patent, however, the engine has a relatively large overall dimension even though it provides a high power output for its displacement. Also, that patent illustrates only a single cylinder engine and in many applications, multiple cylinder engines are desirable.
It is, therefore, a still further object of this invention to provide an improved engine of the type shown in that patent that it has a compact induction and exhaust system and which employs multiple cylinders.
In many applications and particularly those employed in watercraft propulsion systems, a "V"-type configuration is employed for the engine in order to provide a more compact power unit. With the type of engine shown in the aforenoted U.S. Pat. No. 5,377,634, the intake charge is delivered to the crankcase chambers for compression at one side thereof. The compressed charge is delivered to a plenum chamber at the other side of the engine which supplies the intake ports of the engine through intake passages formed in the cylinder head. In addition, an exhaust manifold is also required to collect the exhaust gases and deliver them to the atmosphere. Obviously, these added components and their positions can present problems in conjunction with installation in a marine propulsion system.
It is, therefore, a still further object of this invention to provide an improved engine of the type shown in that patent that it has a compact induction and exhaust systems and which employs multiple cylinders in a "V" type configuration.